Rework standalone to use a synchronous loader that does not invoke Dart code

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index d019d4fcea5bfe401be5ade8377c45bafb5fc291..38da0d42f0d388c4825d62d5370da834f4fd0059 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -2656,10 +2656,10 @@ DART_EXPORT Dart_Handle Dart_SetNativeResolver(
 /* TODO(turnidge): Finish documenting this section. */
 
 typedef enum {
-  Dart_kImportTag = 0,
-  Dart_kSourceTag,
-  Dart_kCanonicalizeUrl,
+  Dart_kCanonicalizeUrl = 0,
   Dart_kScriptTag,
+  Dart_kSourceTag,
+  Dart_kImportTag,
 } Dart_LibraryTag;
 
 /* TODO(turnidge): Document. */